transformed into branched chain fatty acids. There are many steps necessary in order to make branched-chain fatty acids that can be between 12 and 17 carbons in total length. The reaction involves branched-chain fatty acid synthase.
COMPOSITION OF MEMBRANES Fatty acids can be made into phospholipids in order to create the plasma membrane. In total, the plasma membrane is made from lipids and proteins. The phospholipid bilayer forms a stable barrier between the two aqueous compartments (inside and outside the cell). There are several different types of proteins that perform different functions in and out of the cell, including the all-important functions of selective molecular transport and cell-to-cell recognition. There are four major phospholipids in the plasma membrane of animal cells: sphingomyelin, phosphatidyl serine, phosphatidylethanolamine, and phosphatidylcholine. These together make up more than half of the total lipids in the membranes. Interestingly, the makeup of the outer layer is slightly different than the makeup of the inner layer. The outer layer consists of sphingomyelin, phosphatidylcholine, and glycolipids. The inner layer consists of phosphatidylserine and phosphatidylethanolamine. Phosphatidylinositol is also a major part of the inner layer but is not seen much in the outer layer. The head groups of the inner layer are more negatively charged so the inner part of the cell is more negatively charged when compared to the outer layer. Glycolipids and cholesterol are also seen as part of the cell membrane. The glycolipids are found only on the outer layer, with their carbohydrate moieties sticking out of the cell. They represent just about 2 percent of the lipids in the plasma membrane. Cholesterol is a major part of the cell membrane—it makes up about half of the total lipids seen in animal cells. The membrane is relatively impermeable to water-soluble molecules, including ions and most small and large biological molecules. Some fatty acids in the phospholipid molecule are unsaturated and have double bonds that make them hard to pack together. 63
